More Questions Than Answers? Thyroid Biopsy Differs by Specialty

Miriam E. Tucker

June 09, 2021

The likelihood of getting nondiagnostic results from ultrasound-guided fine-needle aspiration (FNA) biopsies of thyroid nodules may vary by specialty, new research suggests.

The nodules biopsied using ultrasound-guided FNAs by radiologists were significantly less likely to be deemed nondiagnostic than those by pathologists or endocrinologists. At the same time, the proportion of nodules that had been discovered incidentally and the percentage that were predominantly cystic were higher among those with FNAs performed by radiologists than the other two specialties.

The data from a study of 356 total thyroid nodules biopsied at a single large academic medical center were presented May 26 in a poster at the American Association of Clinical Endocrinology (AACE) Virtual Annual Meeting 2021 by Christine Chiu, of the University of Southern California (USC) Medical Center, Los Angeles.

Data Don't Mean One Specialty Is Better Than Another

The difference in the nondiagnostic rate may relate to differences in the nodules evaluated, senior author Trevor Angell, MD, also of USC, told Medscape Medical News.

"While we attempted to account for this by comparing the cystic characteristic of nodules, this could not account for all aspects of the nodules evaluated," he said.

"Additional variables that may explain our finding are the use of real-time cytologic assessment, differences in sonographic or procedural techniques, as well as attending supervision, or the experience of the trainees performing the procedures. Most of these possibilities remain unknown and are the subject of ongoing assessment," Angell continued.

But, he added, "These data certainly do not indicate that one specialty performs thyroid nodule FNA better than another, and I do not think a referring clinician should take away any guidance on how to refer patients on the basis of it. We sought to highlight how differences exist within training programs at a single institution."

Asked to comment, endocrinologist David C. Lieb, MD, told Medscape Medical News, "FNA of thyroid nodules is a procedure performed by a number of different types of people...We probably all do it in slightly different ways, and I think there are definitely things we can learn from each other with respect to technique and technology that's used."

Lieb, who is associate professor of medicine at Eastern Virginia Medical School in Norfolk, noted that the reported findings don't include potentially relevant data such as lesion size, location, or the proportion that were repeat biopsies. "It definitely leaves some more questions than answers for me."

He agrees with Angell in that "it doesn't say to me that...if you have a thyroid nodule you should [necessarily] see a radiologist or that a radiology education for FNA is clearly the best and pathologists and endocrinologists are lacking...It generates those questions."   

Nondiagnostic Biopsies Found Less Often by Radiologists

The investigators retrospectively reviewed charts of patients who underwent ultrasound-guided FNAs in 2015-2017 by different teaching services at the same institution, excluding those with hyperthyroidism.

Of the total 356 nodules, 167 were biopsied by radiologists, 119 by endocrinologists, and 70 by pathologists. Onsite cytopathology evaluation was available for radiology and pathology but not endocrinology during that period.

Rates of Bethesda I (nondiagnostic) cytopathology were 3.6% for radiology, 10.1% for endocrinology, and 11.4% for pathology (P < .05).

Lieb called the 3.6% nondiagnostic rate "really low," noting that the 10.1% and 11.4% are closer to his experience and previous reports in the literature.

There were no significant differences between the rates of benign (Bethesda II), indeterminate (Bethesda III-IV), or high-risk (Bethesda V-VI) results.

This was somewhat of a surprise, Angell said. "We anticipated that differing referral patterns may have led to populations of different risk that would lead to different rates of benign, malignant, or indeterminate cytologies, but this was not apparent."

Another significant difference by specialty was the proportion of nodules that had been discovered incidentally rather than by palpation: 58.9% for the radiologists, compared with 43.9% for endocrinology and 32.8% for pathology (P = .001). 

Also different but not quite achieving significance was the proportion of nodules that were partially or predominantly cystic rather than solid. Here, endocrinology had the lowest, 34.6%, versus 53.4% for radiology and 55.5% for pathology (P = .07).

Lieb pointed to a landmark study (J Clin Endocrinol Metab. 2002;87:4924-4927) in which the cystic content of a nodule was found to be the only significant predictor of a nondiagnostic FNA.

"To make a diagnosis, you have to have enough follicular thyroid cells. If it's mostly cystic you're not going to get any cells, just fluid...The more cystic component to the nodule being biopsied, the more likely you're going to get a nondiagnostic FNA result," he explained.

But, he added, given that radiologists actually saw a higher proportion of predominantly cystic lesions than the other two specialties, it would be helpful to have more information about the nodules, such as their size and location. Specifically, he theorized, endocrinologists might be seeing more complicated nodules, or radiologists seeing larger nodules, whereas pathologists may be more likely to perform repeat FNAs.   

The presence versus absence of onsite cytopathology is another notable aspect, Lieb said. "You would assume that the presence of a cytotech would significantly reduce the number of nondiagnostic FNAs that you have…Maybe there was some sort of significant difference in availability of the cytotech or in how frequently they were utilized." 

There were no other significant differences by specialty in patient characteristics such as age, sex, history of Hashimoto's thyroiditis, or history of multinodular goiter.

How Can Diagnostic Rates Be Improved?

Chiu and colleagues conclude that "multidisciplinary ultrasound and procedural training may be helpful for quality improvement of ultrasound-guided FNA performance."

Angell told Medscape Medical News, "We do not have a formalized plan for this, but initially, we may start by simple observation of how other services perform thyroid FNA."

Chiu and colleagues also write: "Limiting nondiagnostic FNA results could lead to improvements in resource utilization, prevention of delays in patient care, and a decrease in performance of procedures with inherent risks."

Angell added that studies looking at issues such as the use of different needle gauge size or core biopsy could provide further information.  

Lieb described a 1-day training course in ultrasound-guided FNA that took place at his institution a couple of years ago that had been organized by yet another relevant specialist — an otolaryngologist.

Endocrinology faculty and fellows were invited to participate. "So it was an opportunity to work together and teach together and learn from each other…I think there's definitely value to that…People fall into silos where they learn how to do something a certain way and they don't fall out of that habit...You learn different techniques from different people."  

Chiu, Angell, and Lieb have reported no relevant financial relationships.

AACE Annual Meeting 2021. Abstract 1003710. Presented May 26, 2021.

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